U.S. patent application number 10/476011 was filed with the patent office on 2004-11-04 for jetting device and a method of jetting device.
Invention is credited to Berg, Johan, Bergman, Mikael, Glazer, Nicholas, Holm, William, Kronstedt, Johan, Lundberg, Marten, Nilsson, Kenth.
Application Number | 20040217193 10/476011 |
Document ID | / |
Family ID | 20283930 |
Filed Date | 2004-11-04 |
United States Patent
Application |
20040217193 |
Kind Code |
A1 |
Holm, William ; et
al. |
November 4, 2004 |
Jetting device and a method of jetting device
Abstract
A jetting device and a method of jetting droplets of viscous
medium onto a substrate. The jetting device includes a jetting
outlet through which the droplets are jetted. The jetting device
further includes a wall located at the jetting outlet, downstream
of the jetting outlet seen in the jetting direction. The wall is
provided with an orifice through which jetted droplets are
permitted to pass through. A gaseous flow is provided within the
space past the jetting outlet such that an adverse effect on the
performance of the jetting device is prevented, the adverse effect
resulting from the accumulation of viscous medium residue at the
jetting outlet.
Inventors: |
Holm, William; (Alvsjo,
SE) ; Nilsson, Kenth; (Akersberga, SE) ;
Kronstedt, Johan; (Sollentuna, SE) ; Lundberg,
Marten; (Hasselby, SE) ; Berg, Johan;
(Uppsala, SE) ; Bergman, Mikael; (Jarfalla,
SE) ; Glazer, Nicholas; (Kallby, SE) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
20283930 |
Appl. No.: |
10/476011 |
Filed: |
February 12, 2004 |
PCT Filed: |
April 25, 2002 |
PCT NO: |
PCT/SE02/00807 |
Current U.S.
Class: |
239/112 ; 239/1;
239/290; 239/423 |
Current CPC
Class: |
B05B 17/0607 20130101;
H05K 3/3485 20200801; H05K 2203/0126 20130101; B23K 3/0607
20130101; H05K 3/305 20130101; B05B 15/55 20180201; B23K 3/0623
20130101; B05C 11/1034 20130101 |
Class at
Publication: |
239/112 ;
239/001; 239/290; 239/423 |
International
Class: |
B05D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 27, 2001 |
SE |
0101503-1 |
Claims
1. A method of jetting droplets of viscous medium onto a substrate,
said jetting device comprising a jetting outlet through which said
droplets are jetted, comprising the steps of providing a gaseous
flow past the jetting outlet such that an adverse effect on the
performance of the jetting device that may result from accumulation
of viscous medium residue at the jetting outlet is prevented,
providing a wall at the jetting outlet, said wall being located
downstream of the jetting outlet seen in the jetting direction, and
providing an orifice in said wall for permitting the jetted
droplets to pass through the orifice, the orifice and the jetting
outlet being aligned in the jetting direction:
2. The method according to claim 1, comprising the step of
providing the orifice with such dimensions that undesired viscous
medium satellites, produced during the jetting of droplets, that
deviate from the general direction of the jetted droplets are
collected by said wall.
3. The method according to claim 2, wherein said gaseous flow is
provided such that viscous medium collected by said wall is removed
from said wall by said gaseous flow.
4. The method according to claim 1, comprising the step of
providing a path for the gaseous flow past the jetting outlet
between said wall and said jetting outlet.
5. The method according to claim 1, comprising the step of
designing said wall so that the gaseous flow adjacent the jetting
outlet is focused and the velocity of the gaseous flow is increased
past the jetting outlet.
6. The method according to claim 4 or 5, wherein said gaseous flow
is provided through said orifice, towards the jetting outlet, and
away from the jetting outlet in a radial direction along the path
provided between said wall and jetting outlet.
7. The method according to claim 6, wherein said gaseous flow is
provided such that a stabilizing effect on the jetting trajectory
of the jetted droplets is obtained.
8. The method according to claim 1, wherein the gaseous flow at the
jetting outlet is directed along a flow path that intersects the
jetting path of the jetted droplets.
9. The method according to claim 8, wherein said gaseous flow
sweeps along the jetting outlet.
10. The method according to claim 8 or 9, wherein said flow path is
essentially perpendicular to said jetting path at the jetting
outlet.
11. A method of jetting droplets of viscous medium onto a
substrate, said jetting device comprising a jetting outlet through
which said droplets are jetted, comprising the step of providing a
gaseous flow past the jetting outlet such that an adverse effect on
the performance of the jetting device that may result from
accumulation of viscous medium residue at the jetting outlet is
prevented, wherein the gaseous flow at the jetting outlet is
directed along a flow path that intersects the jetting path of the
jetted droplets.
12. The method according to claim 11, wherein said gaseous flow
sweeps along the jetting outlet.
13. The method according to claim 11 or 12, wherein said flow path
is essentially perpendicular to said jetting path at the jetting
outlet.
14. The method according to claim 1, wherein the gaseous flow is
provided such that viscous medium residue is removed from the
jetting outlet.
15. The method according to claim 1, wherein said gaseous flow is
provided following the jetting of a series of jetted droplets.
16. The method according to claim 1, wherein said gaseous flow is
provided following a predetermined number of jetted droplets.
17. The method according to claim 1, wherein said gaseous flow is
provided following a predetermined time period during which
droplets have been jetted.
18. The method according to claim 1, wherein said gaseous flow is
provided such that the jetting outlet is kept free of viscous
medium residue.
19. The method according to claim 18, wherein said gaseous flow is
provided during the jetting of said droplets.
20. The method according to claim 1, wherein the gaseous flow is
continuously provided during, between and following the jetting of
droplets.
21. The method according to claim 1, wherein said gaseous flow is
provided such that the presence of undesired viscous medium
satellites produced during the jetting of droplets is reduced, said
satellites being transported away by the gaseous flow.
22. The method according to claim 1, comprising the step of
directing and focusing the gaseous flow adjacent the jetting outlet
such that the velocity of the gaseous flow is increased past the
jetting outlet.
23. The method according to claim 1, comprising the step of
directing and focusing the gaseous flow adjacent the jetting outlet
such that the ability of the gaseous flow to transport viscous
medium residue from the jetting outlet is increased.
24. The method according to claim 1, comprising the step of
providing a suction generator for providing said gaseous flow.
25. The method according to claim 1, comprising the step of
providing a blow generator for providing said gaseous flow.
26. The method according to claim 1, comprising the step of
providing a suction generator and a blow generator in combination
for providing said gaseous flow.
27. The method according to claim 1, comprising the steps of
directing said gaseous flow after having passed the jetting outlet
into a viscous medium waste compartment, and collecting in said
waste compartment viscous medium transported from the jetting
outlet by the gaseous flow.
28. The method according to claim 1, comprising the steps of
directing said gaseous flow through a filter after said gaseous
flow have passed the jetting outlet, and collecting by said filter
viscous medium transported from the jetting outlet by the gaseous
flow.
29. The method according to claim 1, wherein the gas used for
providing said gaseous flow is air.
30. The method according to claim 1, wherein the gas used for
providing said gaseous flow is nitrogen.
31. A method of jetting droplets of viscous medium onto a
substrate, said jetting device comprising a jetting outlet through
which said droplets are jetted, comprising the step of providing an
air flow past the jetting outlet such that an adverse effect on the
performance of the jetting device that may result from accumulation
of viscous medium residue at the jetting outlet is prevented,
wherein said air flow is provided through suction during, between
and following the jetting of individual droplets.
32. A device for jetting droplets of viscous medium onto a
substrate, said device comprising a nozzle having a jetting outlet
through which said droplets are jetted, a flow generator for
producing a gaseous flow, a flow guide for providing a flow path
for said gaseous flow past the jetting outlet, such that an adverse
effect on the performance of the jetting device that may result
from accumulation of viscous medium residue at the jetting outlet
is prevented, wherein said flow guide comprises a wall located at
the jetting outlet, said wall being located downstream of the
jetting outlet seen in the jetting direction, said wall and said
nozzle defining a first space there-between, and a first orifice
provided in said wall, said first orifice and the jetting outlet
being aligned along the path of the jetted droplets, said first
orifice being designed to permit jetted droplets to pass through
said first orifice essentially unaffected, wherein said flow guide
is arranged to provide said gaseous flow within said first space
along a flow path past the jetting outlet.
33. The device according to claim 32, wherein said wall and said
jetting outlet are formed as one integral structure.
34. The device according to claim 32, wherein said first space is
provided with an inlet and an outlet for said gaseous flow.
35. The device according to claim 34, wherein said inlet and said
outlet are provided on opposite sides of the jetting outlet, such
that said gaseous flow intersects the path of the jetted
droplets.
36. The device according to claim 35, comprising a blow generator
communicating with said inlet.
37. The device according to claim 34, wherein said first orifice
constitutes said inlet for said gaseous flow into said first
space.
38. The device according to claim 34, further comprising at least
one second orifice in said wall, said second orifice constituting
said inlet for said gaseous flow into said first space.
39. The device according to claim 34, wherein said flow guide
comprises at least one channel running within said wall for
providing a flow path within said wall for said gaseous flow.
40. The device according to claim 39, wherein said at least one
channel is provided with at least one opening towards said first
space at the jetting outlet, said opening constituting said inlet
for said gaseous flow into said first space.
41. The device according to claim 40, wherein said at least one
opening is directed at the jetting outlet.
42. The device according to claim 32, wherein the dimensions of
said first orifice are such that jetted droplets are permitted to
pass through said first orifice, while viscous medium satellites,
produced during the jetting of droplets, that deviate from the
general direction of the jetted droplets are collected by said
wall.
43. The device according to claim 32, wherein said wall is arranged
to narrow the flow path for the gaseous flow at the jetting outlet
such that the flow velocity past the jetting outlet is
increased.
44. The device according to claim 32, wherein said wall is arranged
to narrow the flow path for the gaseous flow at the jetting outlet,
such that the gaseous flow has an increased ability to transport
viscous medium residue from the vicinity of the jetting outlet.
45. The device according to claim 43 or 44, wherein said wall is
provided with at least one protrusion at said first orifice, said
protrusion being directed towards the jetting outlet for providing
said narrowed flow path.
46. The device according to claim 32, wherein the surface of the
wall facing the substrate and surrounding the first orifice is
bevelled.
47. A device for jetting droplets of viscous medium onto a
substrate, said device comprising a nozzle having a jetting outlet
through which said droplets are jetted, a flow generator for
producing a gaseous flow, a flow guide for providing a flow path
for said gaseous flow past the jetting outlet such that an adverse
effect on the performance of the jetting device that may result
from accumulation of viscous medium residue at the jetting outlet
is prevented, said flow guide being arranged for providing said
flow path in a direction that intersects the jetting path of the
jetted droplets.
48. The device according to claim 47, wherein said flow guide is
arranged for directing said gaseous flow along the jetting
outlet.
49. The device according to claim 47 or 48, wherein said flow guide
is arranged for directing said gaseous flow essentially
perpendicular to said jetting path at the jetting outlet.
50. The device according to claim 32, comprising a filter arranged
downstream of said jetting outlet as seen in the direction of said
gaseous flow, said filter being arranged to collect viscous medium
transported by said gaseous flow.
51. The device according to claim 32, comprising a collection space
arranged downstream of said jetting outlet as seen in the direction
of said gaseous flow, said collection space being arranged for
collecting viscous medium transported by said gaseous flow.
52. The device according to claim 32, wherein said flow generator
comprises a blow generator, and wherein said flow guide is arranged
for providing a flow path from said blow generator and past the
jetting outlet.
53. The device according to claim 32, wherein said flow generator
comprises a suction generator, and wherein said second flow guide
is arranged for providing a flow path between the jetting outlet
and said suction generator.
54. The device according to claim 32, wherein said flow generator
comprises a suction generator and a blow generator, wherein said
flow guide is arranged for providing a flow path between said blow
generator and the jetting outlet, and between the jetting outlet
and said suction generator.
55. The device according to claim 32, wherein the gas used for
keeping the nozzle free of viscous medium residue is air.
56. The device according to claim 32, wherein the gas used for
keeping the nozzle free of viscous medium due is nitrogen.
Description
[0001] This application is the national phase under 35 U.S.C.
.sctn. 371 of PCT International Application No. PCT/SE02/00807
which has an International filing date of Apr. 25, 2002, which
designated the United States of America, the entirety of which is
hereby incorporated by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
jetting droplets of a viscous medium onto a substrate. More
specifically, the invention relates to a method of improving the
performance of a jetting device, and a device for jetting droplets
of viscous medium onto a substrate.
BACKGROUND OF THE INVENTION
[0003] Devices of the above mentioned kind are known and are
primarily intended to be used for jetting droplets of viscous
medium, e.g. solder paste or glue, onto a substrate, e.g. an
electronic circuit board, prior to mounting of components thereon.
An example of such a jetting device is disclosed in WO 99/64167.
The jetting device comprises an eject chamber for containing a
small volume of said medium prior to the jetting thereof, an eject
nozzle communicating with the eject chamber, eject means for
jetting said medium from the eject chamber through the eject
nozzle, and supply means for feeding said medium into the eject
chamber. In WO 00/62587 there is disclosed an assembly comprising
such a jetting device.
[0004] The production speed is an essential factor in the
manufacturing of electronic circuit boards. This has lead to a
desire of increasing the speed at which a substrate is provided
with viscous medium, a way of effecting this is to perform the
actual jetting "on the fly", i.e. without stopping for each
location on the substrate where viscous medium is to be deposited.
A further way to improve the manufacturing speed of electronic
circuit boards is to eliminate or reduce the need for operator
interventions.
[0005] Both of these measures require good and reliable performance
of the device used in the process, as well as a high degree of
accuracy and a maintained high level of reproducibility during an
extended period of time. The high quality requirements of the
electronic industry and the detrimental consequences of errors
appearing in circuit boards even further emphasise these
requirements.
SUMMARY OF THE INVENTION
[0006] Thus, an object of the present invention is to improve the
performance of a device for jetting droplets of viscous medium onto
a substrate.
[0007] This and other objects are achieved according to the present
invention by providing a method of jetting droplets of viscous
medium onto a substrate and a device for jetting droplets of
viscous medium onto a substrate.
[0008] According to a first aspect of the present invention, there
is provided a method for jetting droplets of viscous medium onto a
substrate, said jetting device comprising a jetting outlet through
which said droplets are jetted, comprising the steps of providing a
gaseous flow past the jetting outlet such that an adverse effect on
the performance of the jetting device that may result from
accumulation of viscous medium residue at the jetting outlet is
prevented, providing a wall at the jetting outlet, said wall being
located downstream of the jetting outlet seen in the jetting
direction, and providing an orifice in said wall for permitting the
jetted droplets to pass through the orifice, the orifice and the
jetting outlet being aligned in the jetting direction.
[0009] According to a second aspect of the present invention, there
is provided a method of jetting droplets of viscous medium onto a
substrate, said jetting device comprising a jetting outlet through
which said droplets are jetted, comprising the step of providing a
gaseous flow past the jetting outlet such that an adverse effect on
the performance of the jetting device that may result from
accumulation of viscous medium residue at the jetting outlet is
prevented, wherein the gaseous flow at the jetting outlet is
directed along a flow path that intersects the jetting path of the
jetted droplets.
[0010] According to a third aspect of the present invention, there
is provided a method of jetting droplets of viscous medium onto a
substrate, said jetting device comprising a jetting outlet through
which said droplets are jetted, comprising the step of providing an
air flow past the jetting outlet such that an adverse effect on the
performance of the jetting device that may result from accumulation
of viscous medium residue at the jetting outlet is prevented,
wherein said air flow is provided through suction during, between
and following the jetting of individual droplets.
[0011] According to a fourth aspect of the present invention, there
is provided a device for jetting droplets of viscous medium onto a
substrate, said device comprising a nozzle having a jetting outlet
through which said droplets are jetted, a flow generator for
producing a gaseous flow, a flow guide for providing a flow path
for said gaseous flow past the jetting outlet, such that an adverse
effect on the performance of the jetting device that may result
from accumulation of viscous medium residue at the jetting outlet
is prevented, wherein said flow guide comprises a wall located at
the jetting outlet, said wall being located downstream of the
jetting outlet seen in the jetting direction, said wall and said
nozzle defining a first space there-between, and a first orifice
provided in said wall, said first orifice and the jetting outlet
being aligned along the path of the jetted droplets, said first
orifice being designed to permit jetted droplets to pass through
said first orifice essentially unaffected, wherein said flow guide
is arranged to provide said gaseous flow within said first space
along a flow path past the jetting outlet.
[0012] According to a fifth aspect of the present invention, there
is provided a device for jetting droplets of viscous medium onto a
substrate, said device comprising a nozzle having a jetting outlet
through which said droplets are jetted, a flow generator for
producing a gaseous flow, a flow guide for providing a flow path
for said gaseous flow past the jetting outlet such that an adverse
effect on the performance of the jetting device that may result
from accumulation of viscous medium residue at the jetting outlet
is prevented, said flow guide being arranged for providing said
flow path in a direction that intersects the jetting path of the
jetted droplets.
[0013] For the purposes of this application, it is to be noted that
the term "viscous medium" should be interpreted as solder paste,
flux, adhesive, conductive adhesive, or any other kind of medium
used for fastening components on a substrate, conductive ink,
resistive paste, or the like; and that the term "substrate" should
be interpreted as a printed circuit board (PCB), a substrate for
ball grid arrays (BGA), chip scale packages (CSP), quad flat
packages (QFP), wafers, flip-chips, or the like.
[0014] It is also to be noted that the term "jetting" should be
interpreted as a non-contact dispensing process that utilizes a
fluid jet to form and shoot droplets of a viscous medium from a jet
nozzle onto a substrate, as compared to a contact dispensing
process, such as "fluid wetting", and that the term "gaseous flow"
should be interpreted as a flow of air, compressed air, gas of any
suitable type, such as nitrogen, or any other medium of a gaseous
type.
[0015] Thus, the present invention relates to providing a gaseous
flow at the jetting outlet of a jetting device for preventing an
adverse effect on the performance of the jetting device that may
result from accumulation of viscous medium residue at the jetting
outlet.
[0016] As described above, a jetting device generally comprises an
eject chamber communicating with a supply of viscous medium, and a
nozzle communicating with the eject chamber. Prior to the jetting
of a droplet, the eject chamber is supplied with viscous medium.
Then, the volume of the eject chamber is rapidly reduced, causing a
well-defined amount of viscous medium to be forced with high
velocity out of the orifice or exit hole of the nozzle and onto a
substrate, thus forming a deposit or dot of viscous medium on the
substrate. The jetted amount is hereinafter referred to as a
droplet or a jet.
[0017] During the actual jetting phase, the jetted viscous medium
passes through the orifice of the nozzle and breaks off from the
viscous medium remaining in the eject chamber, thus forming a
droplet or jet travelling towards the substrate. During an
instantaneous moment of the jetting phase, viscous medium passing
the orifice is in contact with the orifice surrounding surfaces of
the nozzle that are most adjacent to and facing the substrate, i.e.
surfaces not being in contact with viscous medium between the
jetting phases. The portion of the nozzle surrounding the orifice
that is adjacent to and facing the substrate is hereinafter
referred to as the "jetting outlet". Thus, the term "jetting
outlet" does not include the portions of the nozzle facing the
eject chamber, i.e. the portions being in contact with viscous
medium between the jetting of droplets.
[0018] When jetting viscous medium, minute amounts of the medium
tend to adhere or stick to the surfaces of the jetting outlet
during the brief moment of contact between the surfaces and the
viscous medium. This occurs due to the characteristics of the
viscous medium. Since it is a requirement that the solder pastes or
other viscous mediums adhere well to a substrate, a so called
tackifier is often used when preparing the viscous medium in order
to achieve the desired adhesiveness. As a consequence, viscous
medium residue may remain attached or adhered to the surfaces of
the jetting outlet following the jetting of a droplet. It should be
noted that viscous medium residue refers to the undesired, often
minute amounts of viscous medium that breaks off from the droplet
during the jetting process. In this context, it refers to the
amounts that has become attached to some surface of the jetting
device after having been ejected out from the eject chamber.
[0019] According to the present invention, a gaseous flow is
provided past the jetting outlet, the magnitude and the velocity of
the gaseous flow being sufficient for transporting viscous medium
residue away from the area at the jetting outlet with the gaseous
flow. Thus, the often minute quantities of viscous medium that
following the jetting of a droplet remains attached to surfaces at
the jetting outlet where no residue is desired is loosened from
said surface and carried away by the gaseous flow. Also, the
gaseous flow provided past the jetting outlet may prevent certain
quantities of viscous medium residue to attach to said surfaces in
the first place.
[0020] As noted above, the presence of viscous medium residue, and
the possible accumulation thereof, at the jetting outlet may have
an adverse effect on the trajectory of the jetted droplets as they
pass the jetting outlet. Also, the viscous medium residue may
interfere with the jetted droplet so as to alter the volume of the
droplet, e.g. a volume of viscous medium residue situated at the
jetting outlet may loosen from the surface and instead adhere to
and be incorporated into the jetted droplet. Furthermore, the
residue may cause spattering of viscous medium when a jetted
droplet "collides" with the residue. Consequently, the presence of
viscous medium residue at the jetting outlet may cause deviations
in the position, form or size of the resulting deposits compared to
that intended. Also, there may be spatters of viscous medium on the
substrate, which spatters may form solder balls that move around
freely on the substrate during reflow and can, in turn, result in
bridging, short circuits, and reduced reliability.
[0021] Thus, the accumulation or build-up of viscous medium residue
has an undesired influence on the jetting performance and,
consequently, on the overall performance of the jetting device.
Particularly, the undesired presence of viscous medium residue at
the jetting outlet will impair the accuracy and the reproducibility
of the device, especially over a period of time, due to the random
build-up of undesired material at the jetting outlet. It may also
lead to inflicted undesired operator interventions, which brings
about interruptions in the manufacturing process and thereby
decreases the overall manufacturing speed.
[0022] Consequently, it is of great importance to prevent a
negative effect on the jetting performance due to accumulation of
viscous medium residue at the jetting outlet. In order to obtain a
high manufacturing speed, it is essential that this negative effect
can be prevented without interruptions in the manufacturing
process. In order to achieve an effective jetting process it is
desirable to provide the gaseous flow in a regulated way. For
example, this can be achieved by providing the gaseous flow after
the jetting of a series of droplets for removing and transporting
away viscous medium residue from the surfaces of the jetting
outlet. According to one example, such a series constitutes a
predetermined number of jetted droplets. According to another
example, the series is made up of the droplets jetted during a
predetermined period of time. Preferably, the gaseous flow is
provided according to a pre-programmed scheme, taken into account
said series of jetted droplets, which scheme is controlled by some
sort of control device.
[0023] Naturally, this can be combined, for example so that the
gaseous flow is provided following a predetermined number of
droplets, but within a predetermined maximum time period. This
means that the gaseous flow is provided at specific intervals,
unless the number of jetted droplets within such a time interval
exceeds a threshold value. If so, there is provided a gaseous flow
and the time interval and number of jetted droplets are reset.
According to another preferred example, the gaseous flow is
provided at each instant when there is no droplet jetted during a
given period of time. At these predetermined "pauses", which can be
the result of substrate exchange or any other reason, the gaseous
flow is provided for removing viscous medium residue from the
surfaces of the jetting outlet.
[0024] As an alternative to the predetermined or pre-programmed
instances for providing the gaseous flow at the jetting outlet, the
gaseous flow can be provided "on demand". Then, there is provided
some sort of detector for detecting whether viscous medium residue
has accumulated at the jetting outlet to such an extent that
gaseous flow should be provided. The detector could be any suitable
detector known within the art, such as a camera.
[0025] According to preferred embodiments of the invention, the
gaseous flow is provided during the actual jetting of the droplets.
Then, the gaseous flow is synchronised with the jetting periods,
i.e. each time a droplet is jetted, there is provided a gaseous
flow at the jetting outlet. Preferably, this is achieved by
providing a continuous gaseous flow throughout the entire jetting
procedure. Alternatively, the gaseous flow is paused at the time
when, or at a predetermined time period after, the jetting process
is halted.
[0026] The provision of a gaseous flow during the jetting of
droplets provides a number of advantages. First, any viscous medium
residue that has become attached to the jetting outlet surfaces
following the jetting of a droplet is immediately transported from
the vicinity of the jetting outlet. Second, the gaseous flow can
pick up and transport away from the jetting outlet minute
quantities of viscous medium that has broken off from the droplet
or jet and that would otherwise adhere to the surfaces of the
jetting outlet as residue. Thus, the build-up or accumulation of
viscous medium residue at the jetting outlet to an adverse amount
is prevented, whereby a high level of accuracy and reproducibility
is maintained during a jetting period.
[0027] A further advantage resulting from the provision of gaseous
flow during the actual jetting of a droplet is that satellites of
viscous medium can be picked-up and transported away from the
vicinity of the jetting outlet. Said satellites being minute
quantities of viscous medium that undesirably breaks away from the
droplet or jet of viscous medium during jetting, thus forming a so
called satellite. Satellites do normally have the same general
direction as the droplet or jet, although with an angular deviation
that causes the satellites to hit the substrate spaced apart from
the intended deposit. These satellites can cause the formation of
solder balls that move around freely on the substrate during reflow
and can, as stated above, result in bridging, short circuits, etc.
Thus, the prevention of viscous medium satellites improves the
result of the application of viscous medium onto the substrate and,
hence, decreases the rejection rate of the completed
substrates.
[0028] A still further advantage of providing gaseous flow at the
jetting outlet during the jetting process is the possibility of
obtaining a stabilizing effect on the trajectory of the jetted
droplet. For example, according to an embodiment of the invention,
the gaseous flow is provided towards the jetting outlet in a
direction opposite that of the jetted droplet, i.e. axially
directed along the jetting path. When reaching the jetting outlet,
the flow is guided such that the flow away from the jetting outlet
is radially directed. Preferably, the axially directed flow is
essentially uniformly distributed, such that an essentially laminar
flow is obtained that has a stabilizing effect on the trajectory or
flight path of the jetted droplets or jets.
[0029] According to the present invention, the gaseous flow is
generated through a flow generator. According to a preferred
embodiment of the present invention, said flow generator is in the
form of suction generator, i.e. in the form of a vacuum ejector or
any other suitable type of suction generator. Said suction
generator then being provided downstream of the area surrounding
the jetting outlet, as seen in the direction of the gaseous
flow.
[0030] An alternative way of producing the gaseous flow, according
to another preferred embodiment of the present invention, is to
provide blow generator, preferably in the form of a source of
pressurised gas or any other suitable type of blow generator. The
blow generator then, of course, being provided upstream of the area
surrounding the jetting outlet. One advantage of providing a blow
generator, as compared to a suction generator, is that a pressure
difference of more than one atmosphere may be obtained.
[0031] According to a specific embodiment of the present invention
a combination of a suction generator and a blow generator is
provided for generating said gaseous flow. Then, the blow generator
and suction generator are suitably provided on opposite sides of
the jetting outlet.
[0032] According to preferred embodiments of the present invention,
there is provided a guide for guiding the gaseous flow to and from
the vicinity of, or the portion surrounding, the jetting
outlet.
[0033] According to preferred embodiments of the invention, the
gaseous flow is directed and focused or concentrated past the
jetting outlet such that the flow velocity is increased to a level
for optimising the transport of viscous medium residue from the
surfaces of the jetting outlet, without adversely affecting the
jetting process. This allows for an effective removal of viscous
medium residue from the surfaces of the jetting outlet and
decreases the possibility of viscous medium residue adhering to the
jetting outlet surfaces, and thereby improves the accuracy and
maintains a high degree of reproducibility during the jetting
process. This can be achieved by providing a narrowed flow path
past the jetting outlet.
[0034] According to embodiments of the first aspect of the present
invention, the jetting device is provided with a wall, the wall
being spaced apart from the jetting outlet and located downstream
of the jetting outlet seen in the direction of the jetted droplets
at the jetting outlet. Said wall may, as an example, constitute
part of a nozzle support, but can be provided without having any
supporting function for the nozzle. Between the wall and the
jetting outlet, there is formed a space acting as a channel or
guide for the gaseous flow at and past the jetting outlet.
[0035] According to a specific embodiment of the invention, the
space formed between the jetting outlet and the wall acts as a
channel for the gaseous flow. In this channel, one end of the space
acts as an inlet, and the opposite end acts as an outlet for the
gaseous flow, said ends being provided at opposite sides of the
jetting outlet. Preferably, the end acting as an inlet communicates
with a blow generator, and the end acting as an outlet communicates
with a suction generator. Alternatively, only the blow generator or
the suction generator, respectively, is provided. The communication
between the space at the jetting outlet and said respective flow
generator are preferably provided through channels, such that the
flow generator can be provided at a distance from the jetting
outlet.
[0036] Since said wall is located in the jetting path, the wall is
provided with an opening or orifice, concentric with the jetting
outlet. The jetted droplets are thereby permitted to pass through
the wall via the orifice. According to a specific embodiment, the
orifice of the wall also functions as an inlet for the gaseous flow
towards the jetting outlet. An advantage of this embodiment is that
a laminar flow can be provided in the manner described above, said
laminar flow having a stabilizing effect on the trajectory of the
jetted droplets or jets. Furthermore, in this embodiment, the
jetted droplets will face a strong head wind immediately following
the jetting thereof. Droplets having a jetting trajectory that
deviates angularly from that intended, will encounter a slight side
wind. The effect of the side wind on a jetted droplet will be
dependent of the magnitude of the angular deviation. As a
consequence, the angular deviation can be enhanced to such an
extent that the jetted droplet will be collected by the wall.
[0037] Alternatively, one or more further orifices may be provided
in said wall, said further orifice(s) then acting as an inlet for
the gaseous flow towards the jetting outlet.
[0038] According to a further embodiment of the invention,
including said wall and the orifice thereof through which the
droplets are jetted, viscous medium satellites, produced during the
jetting of droplets as described above, are prevented from reaching
the substrate. This is achieved by providing said orifice with such
dimensions that, whereas the jetted droplet is permitted to pass
through the orifice, satellites having a direction that deviates
from that of the jetted droplets miss the orifice and are collected
by the wall.
[0039] In the embodiment where the orifice of the wall constitutes
an inlet for the gaseous flow towards the jetting outlet, any
satellites produced will in the same manner as described above, due
to their angular deviation, encounter a side wind that enhances
their angular deviation such that they may be collected by the
wall. Due to the lower velocity and significantly smaller volume of
the satellites, as compared to the viscous medium droplets, the
satellites will be much more susceptible to the effects of the side
wind.
[0040] As understood by the man skilled in the art, the gaseous
flow may be provided such that any viscous medium, e.g. jetted
droplets or satellites, collected by the wall is removed therefrom
and transported away by the gaseous flow.
[0041] According to an example of the present invention, the
focusing of the gaseous flow for optimizing or increasing the
ability of the gaseous flow to transport viscous medium residue
from the jetting outlet is obtained by providing the wall with a
suitable design. According to one embodiment, the wall is provided
with an annular protrusion at and surrounding the jetting outlet
that decreases the area of the flow path and thereby increases the
flow velocity past the jetting outlet. However, as realized by the
man skilled in the art, a vast number of different designs are
possible to obtain the desired increase in flow velocity and
ability to transport viscous medium in accordance with the present
invention.
[0042] Furthermore, the wall may be designed to minimize the
surface area surrounding the orifice onto which viscous medium may
possibly become attached. According to one exemplary embodiment,
this is achieved by providing a bevelled surface around the orifice
on the side of the wall facing the substrate. Then, the inward
orifice surface facing the viscous medium droplet as the droplet
passes the orifice may be significantly reduced, which would reduce
the risk of viscous medium attaching to the wall surface and
negatively affect the performance of the jetting device.
Furthermore, providing a bevelled surface around the orifice will
have the additional advantage of reducing the flow resistance into
the orifice, thereby enabling a more efficient suction and a
reduced risk of turbulence.
[0043] According to an alternative embodiment, the wall is provided
with at least one channel for providing a flow path for the gas
towards the jetting outlet. Then, said at least one channel has an
extension within and along said wall, and is provided with at least
one channel outlet at the orifice of the wall. Preferably, each
channel exit or outlet is arranged such that the gaseous flow is
directed at the jetting outlet. In this embodiment, the gaseous
flow is preferably provided by a blower of some sort, preferably a
source of pressurized gas in communication with the channel(s).
This may of course be combined with a suction device, as understood
by the man skilled in the art.
[0044] According to a further exemplifying embodiment of the
invention, the jetting outlet and the wall are comprised in a
single integral structure. Preferably, the integral structure is
provided with a channel for providing a narrow flow path that
intersects the path of the jetted droplets. Then, the term "jetting
outlet" refers to the portion of the integral structure that faces
the "upper" side of the flow path, i.e. the side of the flow path
facing the eject chamber. As understood by the man skilled in the
art, the wall can be of any suitable form or shape with an orifice,
concentric with the jetting outlet, as described above.
[0045] According to preferred embodiments of the second aspect of
the invention the gaseous flow is provided in a direction
intersecting the path of the jetted droplets. According to a
specific embodiment, the gaseous flow is directed essentially
perpendicularly to the path of the jetted droplets. Preferably, the
gaseous flow is provided past and sweeping along the surfaces of
the jetting outlet.
[0046] It should be noted that according to embodiments of the
second aspect of the present invention, for embodiments that
utilize both a suction generator and a blow generator located on
opposite sides of the jetting outlet, the provision of a wall of
the type described in relation to the first aspect of the invention
is not essential. Thus, there could be provided an open space
between the jetting outlet and the substrate without omitting the
possibility to provide a gaseous flow past the jetting outlet of
sufficient amount and velocity to prevent an adverse effect on the
performance of the jetting device from viscous medium residue at
the jetting outlet.
[0047] According to preferred embodiments of the invention, there
is provided a filter for collecting viscous medium transported from
the vicinity of the jetting outlet by the gaseous flow. The filter
is also provided for preventing viscous medium from ending up in
the suction generator, for the embodiments where such is
provided.
[0048] Furthermore, there may be provided a collection space where
viscous medium transported by the gaseous flow is collected. Then,
collected viscous medium can be collected from the collection space
for reuse. Preferably, the collection space, or waste storage, is
located before the filter, as seen in the direction of the gaseous
flow.
[0049] The jetting device having the features of the present
invention is preferably comprised in an assembly. Then, the flow
generator is preferably located away from the jetting assembly,
communicating with the assembly through a gas or pneumatic
interface, which in turn communicate with the inlet through a
guide, i.e. channels, provided in the assembly.
[0050] Further objects and advantages of the present invention will
be discussed below by means of exemplifying embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] Preferred embodiments of the invention will be described
below with reference to the accompanying drawings, in which:
[0052] FIG. 1 is a perspective view showing the general outline of
a machine for application of solder paste comprising a jetting
device according to the present invention;
[0053] FIG. 2 is a schematic view from above of an embodiment of a
docking device and a jetting assembly of the present invention;
[0054] FIG. 3 is a schematic view showing the underside of the
assembly shown in FIG. 2;
[0055] FIG. 4 is a sectional view of a first embodiment of the
central portion of an assembly comprising a jetting device
according to one embodiment of the present invention;
[0056] FIG. 5a is an alternative sectional view of the embodiment
shown in FIG. 4, and FIGS. 5b and 5c are enlarged sectional views
showing a portion thereof in greater detail;
[0057] FIG. 6a is a similar view as FIG. 5a illustrating an
alternative embodiment of the central portion of the assembly, and
FIG. 6b is an enlarged sectional view showing a portion thereof in
greater detail; and
[0058] FIG. 7 is an enlarged sectional view of an alternative
embodiment of the device according to the invention.
DETAILED DECRIPTION OF EXEMPLIFYING EMBODIMENTS
[0059] FIG. 1 illustrates the general outline of a preferred
embodiment of a machine 1 for providing a substrate 2 with deposits
by dispensing droplets of a viscous medium onto the substrate 2,
i.e. jetting, in accordance with the present invention. For ease of
description, the viscous medium will hereinafter be referred to as
solder paste, which is one of the alternatives defined above. For
the same reason, the substrate will be referred to as an electric
circuit board and the gas will be referred to as air. In this
embodiment, the jetting machine 1 is of a type comprising an X-beam
3 and an X-wagon 4, which is connected to the X-beam 3 via an
X-rail 16 and reciprocatingly movable along the X-rail 16. The
X-beam, in turn, is reciprocatingly movably connected to a Y-rail
17, the X-beam 3 thereby being movable perpendicularly to the
X-rail 16. The Y-rail 17 is rigidly mounted in the jetting machine
1. Generally, the movements are provided by linear motors (not
shown).
[0060] Furthermore, the jetting machine 1 comprises a conveyor 18
for carrying the board 2 through the jetting machine 1, and a
locking device 19 for locking the board 2 when jetting is to take
place.
[0061] A docking device 8 is connected to the X-wagon 4 for
enabling releasable mounting of an assembly 5 at the docking device
8. The assembly 5 is arranged for dispensing droplets of solder
paste, i.e. jetting, which impact and form deposits on the board 2.
The jetting machine 1 also comprises a vision device 7, which in
this embodiment is a camera. The camera 7 is used for determining
the position and rotation of the board 2 and for checking the
result of the dispensing process by viewing the deposits on the
board 2.
[0062] Additionally, the jetting machine 1 comprises a vacuum
ejector 6 arranged on the X-wagon 4, and a source of compressed air
(not shown). The vacuum ejector 6, as well as the source of
compressed air, is in communication with the docking device 8 via
an air conduit interface which are connectable to a complementary
air conduit interface, in this embodiment indicated as input
nipples 9, see FIG. 2, of the docking device 8.
[0063] As understood by those skilled in the art, the jetting
machine comprises a control unit (not explicitly shown) for
executing software running the machine.
[0064] Briefly, the jetting machine works as follows. The board 2
is fed into the jetting machine 1 by means of the conveyor 18, upon
which the board 2 is placed. When the board 2 is in the correct
position under the X-wagon 4, the board 2 is fixed with the aid of
the locking device 19. By means of the camera 7, fiducial markers
are located, which markers are prearranged on the surface of the
board 2 and used to determine the precise position thereof. Then,
by moving the X-wagon over the board 2 in a predetermined
(pre-programmed) pattern and operating the jetting assembly 5 at
predetermined locations, solder paste is applied on the board 2 at
the desired locations.
[0065] With reference to FIGS. 2-3, a preferred embodiment of the
jetting assembly 5, in accordance with the present invention, will
now be described in more detail. The jetting assembly comprises an
assembly holder 11 for connecting the jetting assembly 5 to an
assembly support 10 of the docking device, see FIG. 2. Further, in
this embodiment the jetting assembly 5 comprises a supply container
12 providing a supply of solder paste, and an assembly housing 15.
The jetting assembly 5 is connected to the vacuum ejector 6 and the
source of pressurised air via a pneumatic interface comprising
inlets 42, positioned to interface in airtight engagement with a
complementary pneumatic interface comprising outlets 41, of the
docking device 10.
[0066] With reference now to FIGS. 4-7, the contents and function
of the device enclosed in the assembly housing will be explained in
greater detail. As can be seen in these sectional views, the
jetting assembly 5 includes a jetting device comprising an actuator
locking screw 20 for supporting an actuator in the assembly housing
15, and a piezoelectric actuator 21 formed by a number of thin,
piezoelectric elements stacked together to form an actuator 21,
which is rigidly connected to the locking screw 20. The jetting
device further comprises a bushing 25 rigidly connected to the
assembly housing 15, and a plunger 23 rigidly connected to the end
of the piezoelectric actuator 21, opposite the position of the
locking screw 20. The plunger 23 is axially movable while slidably
extending through a bore in the bushing 25. Cup springs 24 are
provided to resiliently balance the plunger 23 against the assembly
housing 15, and for providing a preload for the actuator 21. An
eject control unit (not shown) applies a drive voltage
intermittently to the piezoelectric actuator 21, thereby causing an
intermittent extension thereof and hence a reciprocating movement
of the plunger with respect to the assembly housing 15, in
accordance with solder pattern printing data.
[0067] Further, the jetting device comprises an eject nozzle 26
operatively directed against the board 2, onto which small droplets
of solder paste are to be jetted. In the nozzle 26, there is
comprised a jetting orifice 27 through which the droplets are
jetted. The surfaces of the nozzle 26 surrounding the jetting
orifice 27 and facing the substrate 2 will be referred to as a
jetting outlet. The plunger 23 comprises a piston portion which is
slidably and axially movably extending through a piston bore 35, an
end surface of said piston portion of the plunger 23 being arranged
close to said nozzle 26. An eject chamber 28 is defined by the
shape of the end surface of said plunger 23, the inner diameter of
the bushing 25 and the nozzle orifice 27. Axial movement of the
plunger 23 towards the nozzle 26, said movement being caused by the
intermittent extension of the piezoelectric actuator 21, will cause
a rapid decrease in the volume of the eject chamber 28 and thus a
rapid pressurization and jetting through the nozzle orifice 27, of
any solder paste contained in the eject chamber 28.
[0068] Solder paste is supplied to the chamber from the supply
container 12, see FIG. 2, via a feeding device. The feeding device
comprises an electric motor (not shown) having a motor shaft 29
partly provided in a tubular bore 30, which extends through the
assembly housing 15 to an outlet 36 communicating via a tubular
bore 31 with said piston bore 35. An end portion of the motor shaft
29 forms a rotatable feed screw 32 which is provided in, and
coaxial with, the tubular bore 30. An essential portion of the
rotatable feed screw 32 is surrounded by an array of resilient,
elastomeric o-rings 33 arranged coaxially therewith in the tubular
bore 30, the threads of the rotatable feed screw 32 making sliding
contact with the innermost surface of the o-rings 33.
[0069] The pressurized air obtained from the above-mentioned source
of pressurized air (not shown) is arranged to apply a pressure on
the solder paste contained in the supply container 12, thereby
feeding said solder paste to an inlet port 34 communicating with
the tubular bore 30. An electronic control signal provided by a
supply control unit (not shown) to the motor causes the motor shaft
29, and thus the rotatable feed screw 32, to rotate a desired
angle, or at a desired rotational speed. Solder paste captured
between the threads of the rotatable feed screw 32 and the inner
surface of the o-rings 33 are then made to travel from the inlet
port 34 to the piston bore 35 via the outlet port 36 and the
tubular bore 31, in accordance with the rotational movement of the
motor shaft 29. A sealing o-ring 22 is provided at the top of the
piston bore 35 and the bushing 25, such that any solder paste fed
towards the piston bore 35 is prevented from escaping from the
piston bore 35 and possibly disturbing the action of the plunger
23.
[0070] The solder paste is then fed into the eject chamber 28 from
an outlet port 36 of the tubular bore 30 via the conduit 31 and a
channel 37. The channel 37 is provided in the piston portion of the
plunger 23, wherein said channel 37 has a first portion extending
axially into said plunger and communicating with the conduit 31,
and a second portion extending coaxially with and within said
plunger 23 from said first portion to the end surface of the
plunger facing the eject chamber 28.
[0071] Turning now to the FIGS. 4-5c, there will be described a
specific preferred embodiment of the present invention. As can most
clearly be seen in FIG. 5b, the jetting device of the jetting
assembly 5 comprises a support plate 14 located below or downstream
of the nozzle orifice 27, as seen in the jetting direction. The
support plate 14 is provided with a through hole 13, through which
the jetted droplets may pass without being hindered or negatively
affected by the support plate 14. Consequently, the hole 13 is
concentric with the nozzle orifice 27.
[0072] According to this embodiment, the jetting assembly 5
comprises an air flow chamber 38 consisting of a first portion
defined by the nozzle orifice 27, the nozzle 26 and the support
plate 14, said first portion defining a disc shaped space
concentric with the piston bore 35; a second portion defined by the
nozzle 26 and the support plate 14, connected to said first portion
and extending coaxially about the nozzle 26; and a third portion
defined by the assembly housing 15 and the bushing 25, connected to
the second portion, parallel with the piston bore 35 and extending
coaxially around the part of the bushing 25 facing said third
portion.
[0073] The air flow chamber 38 communicates with an air flow
conduit 39 located on the side of the piston bore 35 opposite that
of the tubular bore 31. The air flow conduit 39 comprises a first
portion extending from the third portion of the air flow chamber 38
to a second portion of the air flow conduit, said first portion
being parallel with the piston bore 35. Said second portion is in
the form of a bore that is aligned with the conduit 31, and is
arranged to provide a channel between the air flow chamber and a
waste container 50 described below.
[0074] Connected to the jetting assembly 5 is a releasably mounted
waste container 50, for collecting of fragments of solder paste.
The waste container 50 can be best seen in FIG. 5a, where it is
shown in its entirety. The waste container 50 is connected to the
jetting assembly 5 at an interface on the jetting assembly 5, via a
corresponding interface arranged on said waste container 50. The
waste container 50, which will be described in more detail below,
provides an interface and communication between the jetting
assembly 5 and the vacuum ejector 6. Thereby, the negative pressure
or vacuum produced by the vacuum ejector is conveyed to the jetting
assembly 5, and to the communicating air flow conduit 39 and
airflow chamber 38.
[0075] The waste container 50 comprises an air conduit 53, having a
first portion communicating with said connecting interface and
being aligned with the air flow conduit 39 of the jetting assembly,
and a second portion extending perpendicularly from said first
portion. The air conduit 53 communicates with a collection space 55
over a separating wall 54, the collection space being arranged for
collection of solder paste residue removed from the jetting
outlet.
[0076] At the top of the collection chamber 55, a narrow air
conduit 52 leads the air flow from the collection chamber 55 into a
filter 57. The filter 57 is of conventional type and provided for
preventing any fragments of solder paste not collected in the
collection chamber 55 from reaching the vacuum ejector. The filter
is further provided in a longitudinal bore 56 and is in
communication with an outlet conduit 58.
[0077] The waste container 50 is releasably connected to a vacuum
ejector 6, of conventional type, for evacuating the waste container
50. The vacuum ejector 6 is connected to the waste container 50 via
the air outlet 58, a connector 60 and an air tube 61. Even though
the vacuum ejector is illustrated as being separate from the
jetting assembly 5 and/or the waste container 50, a number of other
placements or combinations of the vacuum ejector 6, the jetting
assembly 5, and the waste container 50 are of course conceivable
within the scope of the present invention.
[0078] In operation, the vacuum ejector evacuates the waste
container, including evacuation of the collection space 55 the
narrow air conduit 52, the longitudinal bore 56 and the filter 57,
the outlet conduit 58, the connector 60 and the air tube 61. This
evacuation produces an air flow through the waste container as
indicated by the arrows in FIG. 5a. As a consequence, air flow
conduit 38 and air flow chamber 39 of the jetting assembly 5 are
also evacuated via the interface. Thus, air is sucked in through
the outlet hole 13, which gives rise to a strong air flow in a
direction reverse to that of the jetted droplets. This air flow
will pass the jetting outlet and remove any undesired residue of
solder paste that may have become adhered to the jetting outlet,
for reasons described above.
[0079] According to the present embodiment of the invention, the
air flow is provided before, during and after the jetting of each
droplet. Also, the air flow could also be provided intermittently,
following a predetermined time period of jetting, or following a
predetermined number of jetted droplets. It is also contemplated
that the accumulation or build-up of solder paste residue at the
jetting outlet is monitored, and that the flow of air is provided
when the accumulation reaches a certain level. However, it is
preferred that the air flow is constantly provided during the
jetting process.
[0080] The air will flow through the air flow chamber 38 and
continue into the waste container 50 via the air flow conduit 39.
Due to the force of the air flow, solder paste fragments removed
from the vicinity of the jetting outlet will be transported or
carried through the air flow chamber 38, the air flow conduit 39
and into the waste container 50. Inside the waste container 50, the
air will flow through the air conduit 53, over the separating wall
54 and into the collection chamber 55. Due to the force of gravity,
the majority of the solder paste residue transported by the air
flow will fall into the collection chamber 55, while the air flow
will continue into the narrow conduit 52. Any residue of solder
paste that may continue along with the air flow into the narrow
conduit 52, will be collected by the filter 57, thus preventing
fragments of solder paste from reaching the outlet conduit 58.
[0081] Furthermore, as the jetted droplets face a strong head wind
immediately following the jetting thereof, and droplets having a
jetting trajectory with an angular deviation from that intended,
will encounter a slight side wind. The effect of the side wind on a
jetted droplet will be dependent of the magnitude of angular
deviation. As a consequence, the angular deviation can be enhanced
to such an extent that the jetted droplet will "miss" the hole 13
and instead be collected by the support plate 14. The above may
also be the case for any satellites, described above, which due to
their angular deviation will encounter a side wind and be collected
by the support plate 14. Then, the air flow present or later
produced in the air flow chamber will transport away any solder
paste collected by the support plate 14. Due to the lower velocity
and significantly smaller volume of the satellites, as compared to
the solder paste droplets, the satellites will be much more prone
to be affected by the side wind.
[0082] According to an alternative embodiment of the invention, the
support plate 14 comprises one or more additional holes. Then, the
hole 13 arranged coaxially with the nozzle 27 is primarily used for
providing a path for jetted droplets, while the other hole(s) are
used for providing an inlet of air into the air flow chamber 39.
Naturally, the positioning and design of the other hole(s) must be
such that a forceful flow of air is provided at or past the jetting
outlet.
[0083] According to FIG. 7, an alternative embodiment of a support
plate 114 is illustrated. In this embodiment, the wall of the
support plate 114 is adjacent the hole 113 directed at an angle
towards the jetting outlet. The illustrated design of the support
plate 114 will provide a contraction in the flow path for the air
flow, which will increase the velocity of the air flow immediately
adjacent the jetting outlet. Furthermore, according to this
embodiment, the inward surface of the orifice, i.e. the surface
facing the viscous medium droplet as the droplet passes the
orifice, is very small. This reduces the risk of viscous medium
attaching to the wall surface.
[0084] As realized by the man skilled in the art, a multitude of
alternative designs for narrowing the flow path at or past the
jetting outlet are conceivable without departing from the scope of
the present invention.
[0085] With reference now to FIGS. 6a and 6b, there is illustrated
an alternative embodiment of a device according to the present
invention. Since the general function of the jetting device is the
same as described above, it will not be described further.
According to the present embodiment, a waste container 50 and a
vacuum ejector 6 is mounted to the jetting assembly 5, preferably
releasably mounted. However, there is no interface between the
waste container 50 and the jetting assembly 5. Instead, the air
conduit 53 of the waste container 50 extends to the vicinity of the
nozzle 26 and nozzle 27. The remainder of the waste container as
well as the vacuum ejector are no different from that described
above, and will therefore not be discussed further.
[0086] As described above, a source of pressurized air is connected
to the jetting assembly 5 via a pneumatic interface, the main task
for the pressurized air being described above. According to this
specific embodiment, the pressurized air is also used for providing
a flow of pressurized air at the jetting outlet. This is achieved
by directing a flow of pressurized air from the source, through a
guide (not shown), i.e. air conduits or channels, to a pressurized
air outlet 40 extending to and being directed against the nozzle 27
and the jetting outlet thereof.
[0087] As can be seen in FIGS. 6a and 6b, the outlet of pressurized
air 40 is located opposite the inlet 53 of the waste container 50.
Thus, the blowing effect provided by the pressurized air is
combined with the suction effect of the vacuum ejector 6, which
will transport undesired residue of solder paste from the jetting
outlet. Consequently, there will be a strong air flow across and
intersecting the path of the jetted droplets, which air flow will
transport undesired residue of solder paste from the jetting
outlet.
[0088] Even though the present embodiment has been illustrated
without a support plate, the inclusion of such a plate in this
embodiment is of course conceivable within the scope of the
invention. Then, the flow of air, as indicated by arrows in FIG.
6b, will be present in a chamber or space defined between such a
support plate and the nozzle 27.
[0089] The magnitude of the air flow force will have to be
controlled such that no adverse effects on the jetting trajectory
of the jetted droplets results from the air flow. However, a
constant minor deviation in a given direction can be compensated
for by adjusting the position of the jetting assembly, i.e. the
nozzle, when jetting.
[0090] Even though the present invention has been described above
using exemplifying embodiments thereof, alterations, modifications,
and combinations thereof, as understood by those skilled in the
art, may be made without departing from the scope of the invention,
which is defined in the accompanying claims. For example, the
invention is not restricted to the use of a jetting assembly. On
the contrary, the device and method of the present invention in a
machine for jetting viscous medium without a jetting assembly are
readily realized and comprised within the scope of the
invention.
* * * * *